1. Field of the Invention
The present invention relates to knee joint prostheses, and more particularly, to an implantable knee joint prosthesis including a primary femoral component of modular construction.
2. General Background
In the reconstruction of the anatomical knee joint by total replacement with a prosthetic joint, the femoral, tibial and patellar prosthetic components provide a total knee joint prosthesis in which the contacting surfaces of the components operate to provide a functioning knee joint. At the present time, most total knee prostheses provide for antero-posterior rotation in order to simulate movement similar to the anatomical knee joint with the tendons and ligaments of the joint imparting stability with the component affording a certain degree of stability in the medio-lateral movement. A very common type of knee joint presently utilized is disclosed in U.S. Pat. No. 4,298,992, issued on Nov. 10, 1981 for a "Posteriorly Stabilized Total Knee Joint Prosthesis" wherein there is included a femoral component utilizing a pair of laterally spaced apart condylar portions, each of which having an external surface convexly curved to match generally the lateral profile of the anatomical femoral condyle. U.S. Pat. No. 4,298,992 further discloses a tibial component and a platform portion including spaced apart concavities for receiving each of the condylar portions of the femoral component. The post extends from the tibial plateau into the intracondylar recess of the femoral component so that upon full flexion of the joint, the knee joint is stabilized between the tibial post and femoral recess. The '992 patent addresses the prevention of translocation of the knee during flexion.
During the surgical replacement of a total knee, the surgeon must conduct precise angulated cuts into the femoral condyles of the femur so as to position the femoral component snugly in place so that the joint operates smoothly and is able to undertake the various movements of an anatomical knee. In order to accommodate the femoral component precisely in place, the surgeon is confronted with the problem of having to cut away or "shave" bone that has been worn down or is in a weakened condition unknown to the surgeon until inspection of the bone during the course of the surgery. In order to properly mount the femoral component onto the femur, the weakened or worn portion of the bone must be removed, so that this component can be properly secured to solid bone. The result is that the surgeon may consequently, have to achieve a total knee replacement without having a means to replace greater bone loss than was originally foreseen, resulting in the undesirable condition that the particular leg is slightly shortened by the excessive cutting away of bone and that the location of the prosthetic knee is not precisely in line with the original anatomical knee.